The field of the disclosure relates generally to small molecule inhibitors of protein tyrosine phosphatases (PTPs). Protein tyrosine phosphorylation is a key post-translational modification used by eukaryotic organisms to control protein function. Proper levels of tyrosine phosphorylation are maintained by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Disturbance of the coordinated and opposing activities of PTKs and PTPs leads to aberrant tyrosine phosphorylation, which is associated with the development and pathogenesis of numerous human diseases including cancer, diabetes and autoimmune disorders. Accordingly, dysfunctional tyrosine phosphorylation mediated signaling networks present enormous opportunities for therapeutic intervention. This has prompted the development of inhibitors for disease-associated PTKs, over two-dozen of which have already been approved for clinical use.
For example, mPTPB, a virulence factor of the mycobacterium tuberculosis (Mtb) strain, is a novel drug target of tuberculosis (TB). Tuberculosis continues to be a leading epidemic in the world which kills approximately 2 million and infects 9 million people annually (WHO Report, 2010 on Global TB Control, 2010). The present short course chemo therapy, formulated 40 years ago, starts with administration of isoniazid, pyrazinamide, and rifampicin for two months, and then isoniazid or rifampicin for four months, which is time-consuming, tedious and costly. The emergence of multidrug-resistant (MDR), extensively resistant (XDR), and HIV-associated TB has also severally challenged current therapies (Harries et al., Lancet 2010, 375, 1906-1919; Gandhi et al., Lancet 2010, 375, 1830-1843). With the currently available approaches, it is impossible to eliminate the TB disease as a worldwide threat by reducing incidence below one case per million populations by 2050, a long term target of Millennium Development Goals (Marais et al., Lancet 2010, 375, 2179-2191). In this regard, molecules targeting mPTPB provide a solution for these challenges.
mPTPA is another PTP (17.5 kDa) secreted by the Mtb strain, which has 38% sequence and large overall structural similarities with human low molecular weight PTPs (LMPTP). It has been found that the expression level of mPTPA in M. bovis BCG increased upon entry into stationary phase in vitro or upon infection of human monocytes, implying a positive role of this enzyme during infections. mPTPA is also capable of inhibiting phagocytosis and increasing actin polymerizations in macrophages. Human mPTPA, when combined with its substrate (VPS33B), inhibits phagosome-lysosome fusion, a process arrested in Mtb's infection. A genetic deletion of mPTPA attenuated Mtb growth in human macrophages. These findings indicate that mPTPA is another potential target for the development of novel anti-TB agents, in addition to mPTPB. So far, only few mPTPA inhibitors have been reported, and most of them lack potency and specificity over human PTPs. The compound developed by Ellman (Rawls et al., Bioorg. Med. Chem. Lett. 2009, 19, 6851-6854) based on phosphonodifluoromethyl phenylalanine (F2PMP) as a phosphotyrosine (pTyr) mimetic, with a Ki value at 1.4 μM, is 11-fold selective for mPTPA over LMPTP, and is 70-fold selective for several mammalian PTPs such as PTP1B, TcPTP, CD45.
LMWPTP is a positive regulator of tumor onset and progression probably by dephosphorylating ephrin A2 (EphA2) receptor tyrosine kinase. Clinically, elevated LMWPTP mRNA and protein level have been observed in malignant samples of breast, colon, bladder, and kidney. LMWPTP is also a key negative regulator of insulin signaling, and inhibition of LMWPTP (e.g. by antisense oligonucleotide (ASO) in cultured mouse hepatocytes, liver and fat tissues of diet-induced obese (DIO) mice and ob/ob mice) leads to increased phosphorylation and activity of key insulin signaling intermediates, including insulin receptor-β subunit, phosphatidylinositol 3-kinase, and Akt. Recently, LMWPTP is shown to be a good drug target for cancer and type 2 diabetes Accordingly, small molecule inhibitors of LMWPTP are potential treatments for cancer, insulin resistance, type 2 diabetes and obesity. Unfortunately, the development of LMWPTP inhibitors has met with little success. Moderately active LMWPTP inhibitors have been reported, but these compounds also inhibit other PTPS, such as PTP1B, TcPTP, PTPβ.
Laforin is a dual specificity phosphatase encoded by the EPM2A gene, the mutation of which has been found in patients with Lafora disease, a fatal autosomal recessive genetic disorder characterized by the existence of inclusion bodies (Lafora bodies) in neurons, heart, liver, muscle, and skin. Patients with this disease usually die within 10 years of showing symptoms and do not live beyond the age of 25. Currently there is no cure for the disease. It is proposed that this disease is caused by the mutation in Laforin's carbohydrate binding domain (CBD), making Laforin unable to locate its substrate and eventually leading to the formation of insoluble polyglucocans, the main component of Lafora bodies. Remarkably, whether PTP activity is involved in the development of Lafora disease is one of the open questions in the field, and a specific Laforin inhibitor can provide useful insight.
Further, the Src homology 2 (SH2) domain containing protein tyrosine phosphatase-2 (SHP2), encoded by the PTPN11 gene, has generated considerable interest as an oncology target. Biochemically, SHP2 serves as a positive signal-transducer downstream of most, if not all, receptor PTKs and is required for Ras-ERK1/2 cascade activation. Consistent with its oncogenic potential, germline gain-of-function mutations in PTPN11 cause Noonan syndrome, whereas somatic activating PTPN11 mutations occur in juvenile and adult myeloproliferative diseases and contribute to several types of solid tumors including lung adenocarcinoma, colon and prostate cancer, neuroblastoma, glioblastoma, melanoma, and hepatocellular carcinoma. SHP2 is also shown to play a critical role in both triple-negative and HER2+ breast cancer. Finally, given the essential role of SHP2 in growth factor signaling, thwarting SHP2 action may also prove effective for cancers caused by abnormal activation of receptor PTKs. These findings have spurred an intense effort to develop SHP2 inhibitors for novel anti-cancer agents.
Small molecule inhibitors of PTP are invaluable in elucidating the mechanisms of these diseases and in providing novel therapeutic interventions. However, as discussed above, the development in this area has been largely hurdled by the challenges of developing potent, selective and bioavailable, or simple drug-like PTP inhibitors. The underlying reasons are that more than 100 PTPs identified to date utilize a common catalytic mechanism, and that their highly positively charged active sites share a high level of similarity. Targeting an active site with negatively charged phosphotyrosine (pTyr) substrate mimetics, and surrounding regions with additional fragments is a major strategy having a certain degree of success. pTyr mimetics play a vital role in this regard, and serve as foundations for the development of potent and specific PTP inhibitors. This is well demonstrated by F2PMP, a non-hydrolyzable pTyr mimetic designed nearly two decades ago that led to the discovery of many PTP1B inhibitors to date (FIG. 1).
Carboxylic acid is another typical class of pTyr mimetic that has been studied extensively. Specifically, salicylic acid is a novel, cell permeable pTyr mimetic discovered recently, from which specific inhibitors against LYP, SHP2, and mPTPB have been developed. Consequently, one would consider sulfonic acids as pTyr mimetics in addition to phosphonic and carboxylic acids. Unfortunately, research in this subject had obtained very limited success, with scarce reports on several moderately active and nonspecific PTP inhibitors.
Accordingly, there is a need in the art to provide small molecule inhibitors of PTPs, and more particularly, there is a need for highly potent and specific bioavailable inhibitors of several distinct PTPs, including mPTPA, mPTPB, LMWPTP, Laforin, SHP2, LYP, and HePTP.